[blockly] persistence documentation update (#2427)

* [blockly] persistence documentation update

Signed-off-by: Mark Herwege <mark.herwege@telenet.be>

* review feedback

Signed-off-by: Mark Herwege <mark.herwege@telenet.be>

* fix image filename

Signed-off-by: Mark Herwege <mark.herwege@telenet.be>

---------

Signed-off-by: Mark Herwege <mark.herwege@telenet.be>

configuration/blockly/rules-blockly-persistence.md

@@ -34,40 +34,53 @@ More about that topic can be viewed at ![youtube](../images/blockly/youtube-logo
 
 ![statistical-value](../images/blockly/blockly-persistence-get-statistical-value.png)
 
-_Function:_ computes any of the below functions for the given item since the time provided by _ZonedDateTime_-Block
+_Function:_ computes any of the below functions for the given item since the time provided by _ZonedDateTime_-Block, until the time provided by _ZonedDateTime_-Block, or between 2 timepoints provided by _ZonedDateTime_-Blocks.
 
 openHAB supports history and future values.
 A typical example for future values is a weather forecast.
-Due to adding future values in openHAB the amount of attributes has been vastly increased and the names had to be renamed to become more specific in terms of historic and future states.
+
+For each of the functions, you can choose the output type:
+
+- String: output as a string value
+- Quantity: output as a quantity type with unit
+- Number: output as a number
+- Timestamp: time of the persisted value (when applicable)
+
+![return-type](../images/blockly/blockly-persistence-return-types.png)
 
 **Important:** **Due to a breaking change of the internal methods in openHAB 4.2, Blockly rules that use persistence methods need to be migrated once.**
 This does not happen automatically but needs to be done opening the blockly rule once and re-save it.
 Blockly then automatically rewrites the rule to be compatible.
+When opening the rule, you will be warned it has been created using an older version.
 
 Values:
 
-The following values are available as _historic_ and _future_ representations.
+- persisted state: gets the persisted state at a certain point in time (can be historic or future)
 
-- persisted state: gets the persisted state at a certain point in time
-- average: gets the average value of the State of a persisted Item since a certain point in time.
+The following values are available as _historic_, _future_ and _between_ representations.
+
+![timescope-block](../images/blockly/blockly-persistence-timescope.png)
+
+- average: gets the average value of the State of a persisted Item.
 This method uses a time-weighted average calculation
-- delta: gets the difference in value of the State of a given Item since a certain point in time
-- deviation: gets the standard deviation of the state of the given Item since a certain point in time
-- variance: gets the variance of the state of the given item since a certain point in time
-- evolution rate: gets the evolution rate of the state of the given Item in percent since a certain point in time (may be positive or negative)
-- minimum: gets the minimum value of the State of the given Item since a certain point in time
-- maximum: gets the maximum value of the State of the given Item since a certain point in time
-- sum: gets the sum of the State of the given Item since a certain point in time
+- median: gets the median value of the State of a persisted Item
+- delta: gets the difference in value of the State of a given Item
+- deviation: gets the standard deviation of the state of the given Item
+- variance: gets the variance of the state of the given item
+- evolution rate: gets the evolution rate of the state of the given Item in percent (may be positive or negative)
+- minimum: gets the minimum value of the State of the given Item
+- maximum: gets the maximum value of the State of the given Item
+- sum: gets the sum of the State of the given Item
+- state updates count: gets the count of State updates of the given Item
+- state changes count: gets the count of State changes of the given Item
+- all states: gets all States of the given Item
 
 In the case of the following two functions the block changes its appearance by replacing the time with an option to chose if the equal value should be skipped or not:
 
 ![previous-block](../images/blockly/blockly-persistence-get-previous.png)
 
-- previous state value: Gets the previous state with option to skip to different value as current
-- next state value: Gets the next state with option to skip to different value as current
-- previous state numeric value: same as above but directly returns a number without a unit
-- previous state value time: Gets the time when previous state last occurred with option to skip to different value as current
-- next state value time: Gets the time for which the next state is available with option to skip to different value as current
+- previous state value: gets the previous state with option to skip to different value as current
+- next state value: gets the next state with option to skip to different value as current
 
 The persistence dropdown allows to select the persistence storage from which the value should be retrieved.
 It automatically shows only the storage types that are currently installed on your openHAB instance.
@@ -84,20 +97,48 @@ Notes: in case no or 0 values are retrieved, make sure that the item in question
 
 ![previous-example](../images/blockly/blockly-persistence-get-previous-example.png)
 
-### Check item change / update since a point in time
+### Check item change / update
 
 ![item-change](../images/blockly/blockly-persistence-get-item-change.png)
 
-_Function:_ checks if an item was updated or changed since a certain point in time
+_Function:_ checks if an item was updated or changed since the time provided by _ZonedDateTime_-Block, will be updated or changed until the time provided by _ZonedDateTime_-Block, or between 2 timepoints provided by _ZonedDateTime_-Blocks.
+
 Type: boolean `true` or `false`
 
-### Provide last updated date of an Item
+### Provide last or next updated or changed date of an Item
 
 ![item-updated-date](../images/blockly/blockly-persistence-updated-date.png)
 
-_Function:_ Provides the last updated date (including time) of an Item
+_Function:_ Provides the last or next updated or changed date (including time) of an Item
 Type: ZonedDateTime
 
+### Persist State or States for an Item
+
+Persist State or States for an Item.
+
+Multiple options are available:
+
+- state (at current time): persist given State at the current time
+
+Following options are not supported by all persistence services (for example the standard rrd4j does _not_ support this).
+
+- state (at specific time): persist given State at given time
+- list of states (adding): persist list of States, not replacing the already persisted States.
+- list of states (replacing): persist list of States, replacing the already persisted States in the same time period
+
+As an example for persisting a list of States, one could calculate timephased future values such as expected electricity availability below a specific price point from multiple inputs, and store these in one operation as a future timeseries.
+The adding operation would keep what is already in persistence, while the replacing operation would replace anything already in persistence for the item between the first and last timestap in the series.
+With a forecast persistence strategy, these future persisted values of the item would become actual values as time moves forward.
+
+The _list of states_ input is a Blockly _List_ of _List_.
+The inner _List_ represent pairs of time provided by a _ZonedDateTime_-Block and a _String_ representation of the State.
+
+### Remove all States for an Item
+
+Remove all States for an Item since the time provided by _ZonedDateTime_-Block, until the time provided by _ZonedDateTime_-Block, or between 2 timepoints provided by _ZonedDateTime_-Blocks..
+
+This is not supported by all persistence services (for example the standard rrd4j does _not_ support this).
+
 ## Return to Blockly Reference
 
 [return to Blockly Reference](index.html#persistence)